Semiconductor substrates are generally stored and transported in substrate storage cassettes. A typically substrate storage cassette includes a plurality of substrate support slots arranged to hold substrates in a spaced-apart, vertically-stacked orientation within a housing. In many systems, the housing, also known as a pod, includes a sealable door that allows the substrate stored within the cassette to be isolated from the surrounding environment. The ability to isolate the interior of the substrate storage cassette from the surrounding environment is particularly important when substrates are transported between fabrication tools in order to minimize potential particulate contamination.
Substrate storage cassettes are typically coupled to a fabrication tool at a factory interface. The factory interface includes one or more bays, each configured to accept one substrate storage cassette. In order to maintain isolation of the environment surrounding the substrates stored inside the substrate storage cassette, each bay is equipped with a pod door opener (PDO). The PDO the door of the pod from within the factory interface while maintaining a seal between the factory interface and the substrate storage cassette, thus maintaining isolation of the substrates from the surrounding environment.
Occasionally during the docking and door-opening procedure, one or more of substrates within the substrate storage cassette may inadvertently move laterally toward the factory interface. Once the substrate is moved out of position within the substrate storage cassette, the substrate is highly likely to become damaged or create other processing problems. For example, a misaligned substrate may be hit by another substrate being removed or returned to the substrate storage cassette, thereby causing damage to one or both of the substrates. Additionally, the misaligned substrate may not be positioned correctly on the blade of the transfer robot, thus potentially becoming disengaged from the robot blade during transfer, or becoming misaligned or damaged while being positioned in the next transfer area, or creating orientation/alignment problems during substrate processing.
Therefore, there is a need for a method and apparatus for operating a pod door to mitigate substrate misalignment and prevent substrate damage.